NOTE: This a revision to the previous article on Adding 4th, 5th,and 6thHarmonicPercussion. In this article, the 2nd and 3rd harmonics have been added and the switching schematic for harmonic selection is much simpler.
Adding Polyphonic Percussion For 2nd, 3rd, 4th, 5th and 6th Harmonics to the Hammond (B3, C3, RT3 or A100) allows for much more percussion variation by making 3 more polyphonic harmonics available in addition to the 2nd and 3rd standard harmonics. Using the first 3 drawbars, (the usual setup) there is much more contrast between the drawbar setting and the percussion tones when the upper percussion harmonics are added. The sharp percussive bite is now effective much lower on the keyboard. All harmonics (2 through 6) are controlled independently and may be selected in any combination. For example, the 2nd and 5th or the 2nd and 6th harmonic give a nice “twin mallet” xylophone tone.
To get the full effect of this harmonic addition EliminatingThePercussionVolumeDrop is very desirable since this will restore full volume control to the drawbar settings. Five miniature toggle switches select the desired harmonic for percussion. Note with this design, the selected percussion harmonic is not available at the drawbars. An additional feature; if a harmonic is selected via a toggle switch, there is no percussion decay when the “B” preset is on and the left most percussion tablet is off (ParadiseButton). The result is a sustained sharp attack for any of the 5 selected harmonics. Note, when all five toggle switches are off, the 2nd and 3rd harmonic percussion features are identical to the original stock Hammond
DESIGN SCHEMATIC—POLYPHONIC PERCUSSION
The previous design of the 2nd, 3rd, 4th, 5th And 6th harmonic addition required two 3PDT switches. The circuit design below requires only DPDT switches (5 total). In addition, if the 2nd or 3rd harmonic is selected via the toggle switches, these harmonics are now returned to the drawbars. The harmonic returned is determined by the selection on the 2nd/3rd percussion rocker tablet.
The schematic below shows five switches S2, S3, S4, S5 and S6 for harmonic selection. S2 and S5 are shown in the ON state. This selects the 2nd and 5th harmonic. S3, S4 and S6 are shown in the OFF state.
<pre>
|----|----------------|--------------|----------|-----------|
| | | | | |
| | | | | |
| .\ .--| . /.-| . /.-| .\ .--| . /.-|
| \S2-1 | S3-1/ | S4-1/ | \S5-1 | S6-1/ |
| . | . | . | . | . |
| | | | | | | | | | |
| | | | | | | | | | |
| TS2W TS2 TS3W TS3 DB6W DB6 DB7W DB7 DB8W DB8
| 2nd Harm 3rd Harm 4th Harm 5th Harm 6th Harm
|
|
|
| .\ .--| . /.-| . /.-| .\ .--| . /.-|
| \S2-2 | S3-2/ | S4-2/ | \S5-2 | S6-2/ |
|-------. | . | . | . | . |
| | | | | | | | | |
| | | | | | | | | |
| |------| |-----| |------| |-----| |
| |
H HW
</pre>
S2 2nd harmonic DPDT On/Off switch; Mouser Part No. 633-M202201
S3 3rd harmonic DPDT On/Off switch; Mouser Part No. 633-M202201
S4 4th harmonic DPDT On/Off switch; Mouser Part No. 633-M202201
S5 5th harmonic DPDT On/Off switch; Mouser Part No. 633-M202201
S6 6th harmonic DPDT On/Off switch; Mouser Part No. 633-M202201
H AO28 percussion amplifier input terminal
HW Green wire that was on terminal H
TS2 Terminal strip (on back of manual) where 2nd harmonic comes from manual
TS2W Yellow wire from the B preset that was on TS2
TS3 Terminal strip (on back of manual) where 3rd harmonic comes from manual
TS3W Green wire from the B preset that was on TS3
DB6 Drawbar 6 terminal (4th Harmonic)
DB6W Blue wire that was on Drawbar 6
DB7 Drawbar 7 terminal (5th Harmonic)
DB7W Violet wire that was on Drawbar 7
DB8 Drawbar 8 terminal (6th Harmonic)
DB8W Gray wire that was on Drawbar 8
INSTALLATION
Five miniature toggle switches need to be mounted. They can be mounted in a row to the bottom of the front wood rail using a small angle bracket. Highlights of the required wiring are as follows:
<pre> *Unsolder~* Blue, Voilet, and Gray wires on Drawbars 6, 7 and 8. Solder new wires to the wires removed from the Drawbars (DB6W, DB7W and DB8W) and route to the five toggle switches. Solder new wires to the Drawbars (DB6, DB7 and DB8) and route to the five toggle switches. *Unsolder~* Yellow and Green wires on Terminal Strips 2 and 3 Solder new wires to the wires removed from the Terminal Strips (TS2W and TS3W) and route to the five toggle switches. Solder new wires to the Terminal Strips (TS2 and TS3) and route to the five toggle switches. *Unsolder~* Green wire on Terminal H on AO28 Solder new wire to the wire removed from the Terminal H (HW) and route to the five toggle switches. Solder new wire to Terminal H on AO28 (H) and route to the five toggle switches. </pre>
Solder all of the wires routed to the five toggle switches per the above schematic. Also solder all the remaining “jumpers” shown on the schematic. These “jumpers can all be soldered locally at the five switches.
Here’s a picture showing the installation of the five harmonic selectors switches under the front rail. The percussion switches are on the right.
THEORY OF OPERATION
The function of the toggle switch contacts is as follows: The “1” set of contacts selects the appropriate harmonic from the drawbar or terminal strip wire and routes it to the “H” (percussion input on AO-28) terminal. The “2” set of contacts are wired in series to isolate “HW” from terminal “H” anytime a harmonic is selected.
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